Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.70	7.234%	$31.8485	$31.85	$31.85	$31.80
Purchase #2	$92.29	9.196%	$100.777	$100.78	$100.80	$100.80
Purchase #3	$162.81	4.365%	$169.9167	$169.92	$169.90	$169.90
Purchase #4	$175.56	5.700%	$185.5669	$185.57	$185.55	$185.60
Purchase #5	$137.43	6.674%	$146.6021	$146.60	$146.60	$146.60
Purchase #6	$214.98	13.548%	$244.1055	$244.11	$244.10	$244.10
Purchase #7	$239.46	4.183%	$249.4766	$249.48	$249.50	$249.50
7 purchase totals =	$1,052.23		$1,128.2933	$1,128.31	$1,128.30	$1,128.30